Artificial blood vessels are artificial organs used for the purpose of circulation repair in the field of vascular surgery. Since artificial blood vessels have the characteristic of being permanently implanted in the body, particularly rigid standards are required with respect to safety. In addition to not changing in size (e.g. dilation), not causing the occurrence of new aneurysms, ruptures and so forth, they are also required to have bioaffinity and be composed of materials having histocompatibility. As predecessors of the artificial blood vessels of today, artificial blood vessels for medical use have been developed over the past forty years and are currently available on the market. These include artificial blood vessels made of PET, those made of drawn polytetrafluoroethylene film (EPTFE) and those originating in living tissue. Other examples of products that have been developed include knit or woven artificial blood vessels made of PET (trade name: Dacron) or PTFE (Teflon), those in which artificial blood vessels are coated with collagen or gelatin (Hemashield or Zeroseal)in order to prevent bleeding from the mesh of these woven artificial blood vessels immediately after their replacement, and those that prevent bleeding and thrombus formation inside the vessel by coating the mesh of these woven artificial blood vessels with albumin. Artificial blood vessels made of EPTFE (trade name: Goatex) offer the advantage of making it difficult to form thrombi. On the other hand, with respect to those originating in living tissue, although there are some examples for which satisfactory patency is obtained by treating dog artery with surfactant (see Brandel, et al., Japanese Provisional Patent Publication No. 60-501540) to form a connective tissue tube followed by homotransplantation, these are still only at the experimental stage. In humans, although body tissue is used for transplantation by taking out congenic arteries and veins from cadavers followed by storing after freezing gradually to reduce isoimmunization, it is actually essential to use an immunosuppressant to avoid rejection. In addition, artificial blood vessels have also been developed in which human umbilical cord vein is crosslinked with a crosslinking agent, after which the outside thereof is coated with an extremely coarse Dacron mesh.
On the other hand, collagen is also known as a medical material, and this is used in combination with living tissue originating and artificial materials (see Japanese Provisional Patent Publication No. 2-109569 and Japanese Provisional Patent Publication No. 7-116242). Collagen has excellent bioaffinity, histocompatibility and low antigenicity, as well as action that promotes host cell extension and growth. It also has hemostatic action and is completely absorbed in the body. This collagen is obtained by extracting from various animals, and insoluble collagen is treated with base or enzyme. However, extracted collagen is in the form of monomers and oligomers at the molecular level, and is broken down extremely rapidly in water, humor and blood. Consequently, in order to use these collagens as medical materials, it is necessary that they be crosslinked with a crosslinking agent, gamma rays, ultraviolet rays, electron beam or heat to give them suitable physical properties prior to use. However, the use of powerful crosslinking agents results in a loss of the biochemical properties of the collagen. What is more, even if crosslinked in this manner, there is hardly any improvement in the tear strength of other physical properties of the collagen material. Consequently, in the case of using collagen in combination with other materials as an artificial organ, the needle holes in the sutured surface after being transplanted in the body end up enlarging as a result of being unable to withstand the load, ultimately resulting in rupture. As is indicated by this example, it has not been possible to produce products requiring specific physical properties. Artificial blood vessels composed by combining collagen with other materials also have the disadvantage of the sutured portion not being maintained for a long time in the body.